Exemplary embodiments of the invention relate to a fuel cell stack.
Fuel cell units convert chemical energy into electrical energy. A fuel cell unit is customarily composed of a membrane electrode unit having a proton-conductive membrane, and as electrodes, an anode and a cathode in the form of gas diffusion electrodes, the membrane being situated between the anode and the cathode, and the membrane electrode unit being situated between two bipolar plates, and a bipolar plate in each case being situated between two adjacent fuel cell units.
Since a voltage that can be generated by a single fuel cell unit is relatively small, multiple fuel cell units are typically coupled to one another and combined as a fuel cell stack. The stacked fuel cell units are generally situated in a housing, which is preferably situated between end plates of the fuel cell stack. In addition, in this arrangement at least one side of the end plates is accessible in such a way that a force-fit connection to a holder or support frame, such as a vehicle body, may be established. The height of a fuel cell stack having a predefined number of fuel cell units may vary due to thickness tolerances of the bipolar plates, the membrane electrode units and/or the seals, for example. The thickness deviations of the individual components vary, for example, in a range from several hundredths of a millimeter to several tenths of a millimeter. Since the individual tolerances of the components are cumulative, the height of the fuel cell stack containing several hundred fuel cell units, for example, may deviate greatly from a target height. For example, tolerances in the range of ±5 millimeters, in individual cases even ±17 millimeters, are known. As a result, the height of each housing must be individually adapted to the height of the fuel cell stack.
To solve this problem, for example numerous housings having different heights are produced in advance, and an appropriately sized housing is introduced into the production process as soon as the height of the corresponding fuel cell stack is known.
Japanese patent document JP 2009170169 discloses a fuel cell stack situated in a housing having a cover element on its longitudinal sides, and is closed off on an end-face side by an end plate. The cover element and the end plate extend in parallel in sections, and a seal is situated in the section extending in parallel.
Exemplary embodiments of the present invention are directed to a fuel cell stack that is improved over the prior art.
A fuel cell stack is formed from a plurality of stacked fuel cell units and at least one stack end element, the stacked fuel cell units being surrounded by a housing. According to the invention, a frame element is situated on the at least one stack end element and the housing on the end-face side, at least one seal being situated at least between the stack end element and the housing in the area of the frame element.
As described above, the height of the fuel cell stack may vary due to thickness tolerances of the bipolar plates, the membrane electrode units, and/or the seals, for example. Such height differences may advantageously be compensated for by means of the frame element. For this purpose, the frame element encompasses the stack end element and the housing on the end-face side, so that by means of the at least one seal, seal-tightness between the housing and the stack end element is ensured, even for large height tolerances. Thus, housings having standardized heights are preferably usable so that installation may be carried out in a cost- and time-efficient manner.
The frame element is advantageously secured on an end-face side of the stack end element and an end-face side of the housing in a positive-fit, force-fit, and/or integrally joined manner. The frame element is preferably mounted in a positive-fit manner on the end-face side of the stack end element and of the housing, the positive fit being assisted by appropriate adhesive bonding and/or screw connections, thus ensuring a mechanically stable connection between the frame element and the stack end element as well as the housing.
In one possible embodiment, the end-face side of the stack end element is formed by a circumferential angled border of the stack end element, the end-face side of the stack end element extending parallel to the end-face side of the housing and in the stack direction. The flexural and torsional strength of the stack end element are advantageously increased by means of the angled border of the stack end element.
For an optimal positive fit with the end-face side of the stack end element and the housing, in one possible embodiment the frame element has a U-shaped profile, the length of the legs of the U-shaped profile corresponding to the length of the angled end-face side of the stack end element, so that the frame element encompasses the end-face side of the stack end element.
In a first embodiment of the invention, two seals oriented in parallel to one another and having a U-shaped profile in each case are situated between the legs, one of the seals surrounding the end-face side of the stack end element, and the other of the seals surrounding the end-face side of the housing. A positive fit and a seal of the stack end element with respect to the housing are thus advantageously possible. The seals are preferably molded onto the inner surfaces of the frame element, and therefore are easily producible.
It is particularly preferred that the U-shaped profile of one of the seals has a design corresponding to the shape and/or external dimensions of the end-face side of the stack end element, and that the U-shaped profile of the other seal has a design corresponding to the external dimensions of the end-face side of the housing. The seal for accommodating the end-face side of the housing is formed in such a way that this seal is able to accommodate end-face sides of housings having different heights in a predefinable height range.
In a second embodiment of the invention, the surface side of the end-face side of the stack end element facing in the direction of the housing is provided with a seal. The seal is formed from a plurality of lip seals, for example. When the housing is mounted on the fuel cell stack, i.e., when the housing is pushed on in the stack direction, a good sealing effect is thus already achieved. In order to improve a resulting contact pressure, the frame element is situated on the end-face side of the stack end element and of the housing, and thus acts as a clamping frame.
The seal preferably has recesses for accommodating a clamping device, the clamping device being electrically insulated at least in the area of the recesses. The seal, which is designed as a lip seal, for example, and the electrically insulated clamping device advantageously cooperate in a sealing manner, and thus prevent penetration of moisture into the area between the fuel cell stack and the housing. The combination of the clamping device for clamping the fuel cell stack and the seal of the stack end element with respect to the housing also allows simple and cost-effective production of a sealing system for the fuel cell stack, and also saves installation space. For electrically insulating the clamping device, insulation is formed, preferably molded, onto the clamping device by means of an injection molding process, for example.
To optimize the sealing effect of the insulation of the seals, the seals are made of a rubber, a foam, polyvinyl chloride, thermoplastic polyurethane, and/or a thermoplastic polymer. These electrically insulating materials are characterized by high chemical resistance, high heat resistance, and good corrosion properties.
Mutually corresponding parts are provided with the same reference numerals in all the figures.